Just completed a top end overhaul on Mercruiser 4.3 ( 2 new valves, seats and valves re-ground, manifolds skimmed, new carb kit, bores honed and new big end bearings) the bearings weren't bad and there was no knocking before doing the work, the reason for the work was because of a serious backfire throught the carb and power loss, found a "tide Mark" in a cylinder bore and intake manifold from water ingress through the winter layup. To cut a long story short, after only 4 hours running the new bearings are toast, especially 2 of them and the crankshaft journals are beyond a re-grind (the engine was a re-con block fitted in 2008 and had
0.010" oversize bearings) engineer said it wouldn't grind any more?) what might have caused this failure of the bearings. Oil pressure and temperature has been good (except at time of sudden failure when pressure dropped off) oil and filter was new, level ok. What we did find was that the main bearings were stamped 0.25mm and the new big end bearings were 0.010" (calculator says 0.010" = 0.254mm) engine expert said that difference would not cause the failure.
0.010" oversize bearings) engineer said it wouldn't grind any more?) what might have caused this failure of the bearings. Oil pressure and temperature has been good (except at time of sudden failure when pressure dropped off) oil and filter was new, level ok. What we did find was that the main bearings were stamped 0.25mm and the new big end bearings were 0.010" (calculator says 0.010" = 0.254mm) engine expert said that difference would not cause the failure.